How are money percentages determined?

I frequently see public % and money % on a bunch of different websites suggesting picks. How is this data acquired? Are all bets on the big sportsbooks made public? Can these 3rd party websites literally see if someone made a $10,000 bet on team X? I'm just curious as to how websites like Action or VSiN get their data. Why would the sportsbooks agree to give them this data? Are they required to make all bets public somewhere? Any insights would be much appreciated.